The present disclosure relates to an image processing device and an image processing method which process a high dynamic range image, and to an image display device.
Recently, according to the increasing bit-depth of imaging elements (imaging sensors), there is progress in the adoption of high dynamic range (HDR) images. An HDR image has a contrast ratio between the maximum brightness color and the minimum brightness color of, for example, 10000:1 or greater, and can realistically represent the real world. The HDR image has merits such as being capable of realistically representing shading, being capable of simulating exposure, and being capable of representing glare. Incidentally, a standard dynamic range (SDR) image generally has a contrast ratio of, for example, 1000:1, 256:1 or lower, has a low dynamic range, and is often expressed using 256 grades of device primary colors such as red, green, and blue, or cyan, magenta, and yellow.
For example, an imaging device which synthesizes an HDR image from a plurality of imaged images with different exposures is proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2013-255301).
A camera used in the image production of television programming or the like normally has a function of capturing HDR images. However, many household television receivers used to view the television programming do not support HDR images. Therefore, even if the camera used in the image production is capable of capturing HDR images, in practice, the HDR image is converted into an image with a compressed dynamic range, edited, and subsequently transmitted as a broadcast signal in consideration of the fact that the compressed image can be displayed as it is by a household television receiver, that is, in consideration of downward compatibility. A master monitor that is used for editing the image by the broadcasting station has a white luminance of approximately 100 nits, the high luminance information that is captured is compressed, gradation is damaged, and the sense of presence is lost.
Incidentally, on a general household television, a dynamic range that is reduced to approximately one fortieth, for example, is standard, that is, standard dynamic range (SDR). The SDR image has a contrast ratio of, for example, 1000:1, 256:1 or lower, has a low dynamic range, and is often expressed using 256 grades of device primary colors such as red, green, and blue, or cyan, magenta, and yellow.
It is possible to convert an HDR image into an SDR image using Knee compression. Knee compression is a process of suppressing a high luminance portion of a signal such that the luminance of the image is kept within a predetermined dynamic range (here, the SDR dynamic range). For example, an imaging device which subjects an image signal that is output form an imaging element to Knee compression and keeps the dynamic range within a predetermined luminance level is proposed (for example, refer to Japanese Unexamined Patent Application Publication No. 2007-208382).
Recently, the commercial sale of displays which support HDR in which the maximum luminance is 500 nits or 1000 nits started. However, as described above, even though the image is originally an HDR image, since the image is broadcast as an SDR image, the waste of viewing the SDR image using an HDR supporting television occurs.